Conventionally, there have been known a method and apparatus for starting a turbine generator with an inverter which controlled by a microprocessor, in which a motor installed on a shaft of a gas turbine is driven by an external power supply through the inverter, and AC power generated from the turbine generator is supplied through the inverter to power lines of the external power source after the time the started gas turbine switches to an autonomous working operation.
Another known gas turbine starting apparatus can start a gas turbine, in a simple mechanism as compared with an inverter, using an AC power supply without any change made to a DC motor installed in the gas turbine (for example, see Japanese Patent Public Disclosure (Kokai) No. 2001-254635 (particularly, Paragraph [0011] and FIG. 1).
However, since a-gas turbine is generally rotated at high operation speeds, a high voltage-resistant rectifier circuit is required for converting AC power generated from a turbine generator to DC power, and a large scaled circuit is also required for an inverter to tolerate high frequencies.
On the other hand, some devices incorporated in a power generation system should be controlled at variable speeds, so that a general-purpose inverter is also needed. However, such an inverter is limited in its utilization.